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Numbers k such that k and k^2 use only the digits 1, 2, 8 and 9.
0

%I #11 May 10 2024 09:26:16

%S 1,9,11,91,911

%N Numbers k such that k and k^2 use only the digits 1, 2, 8 and 9.

%C Generated with DrScheme.

%C No additional terms through 10^10. - _Harvey P. Dale_, Jul 04 2012

%H Jonathan Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived]

%e 911^2 = 829921.

%t okQ[n_]:=Module[{u=Union[IntegerDigits[n^2]]},And@@Table[MemberQ[ {1,2,8,9}, u[[i]]],{i,Length[u]}]]; Flatten[Table[ Select[FromDigits/@ Tuples[{1,2,8,9},x],okQ],{x,10}]] (* _Harvey P. Dale_, Jul 04 2012 *)

%K base,nonn,more

%O 1,2

%A Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008